1. Field of the Invention
The present invention relates to a stabilized cosmetic or dermatological composition containing several compounds capable of releasing the same active agent or compound in contact with the skin, including the scalp. The active agents to which the invention applies are all the compounds which are usable in the cosmetic and/or dermatological field for which bioconvertible precursors exist. This composition may be applied to the human body and/or face.
As active agents, special mention may be made of vitamins, lipopeptides, lipoamino acids, .alpha.- and .beta.-hydroxy acids (lactic, glycolic, glucuronic acid), antioxidants such as flavonoids (for example, quercetin or rutin), catechins, of which the natural extracts of plants such as tea are composed, and hydrating agents such as polyols (glycerol).
2. Discussion of the Background
There is increasing interest in introducing vitamins such as vitamins A, B, C, D, E and F (essential fatty acids), as well as other active agents, into cosmetic and/or dermatological compositions with a view to providing specific treatments against, for example, excessive weight, skin aging, dry skin, skin pigmentation, acne and certain skin diseases (psoriasis) or, alternatively, in order to promote the cicatrization (scar formation) and/or restructuring of the skin.
In particular, the application of a sufficient amount of ascorbic acid or vitamin C to the skin enables the growth of the connective tissue and, in particular, that of collagen to be stimulated. Ascorbic acid also enables the defenses of the cutaneous tissue against harmful external agents such as ultraviolet rays or pollution, or the adverse effects of medicinal products, alcohol or tobacco, to be strengthened.
Moreover, tocopherols, such as vitamin E, are known to possess both antioxidant properties with respect to cell membrane phospholipids and anti-free-radical (AFR) properties (see "Radicaux libres et Vitamine E", that is "Free radicals and vitamin E" by J. B. Chazan and M. Szulc -Cah. Nutr. Diet. 1987 6 XXII-1- pages 66-76).
In addition, vitamin A or retinol, and also hydroxy acids, are known to combat aging. Furthermore, vitamin A is known to effect cicatrization of the skin.
Unfortunately, most of these active agents (vitamins, antioxidants, hydroxy acids, and the like) are unstable in solution and sensitive to external factors, rendering these solutions ineffective and detracting from the desired efficacy.
The article "Stability of ascorbic acid" by Br. Hajratwala, published in "Sciences Pharmaceutiques Revue" pages 281-286, teaches that ascorbic acid possesses properties of instability in an aqueous medium, in an aerobic and anaerobic medium, with a more marked instability in an aerobic medium. This publication includes an illustration of the behavior of ascorbic acid in the presence of changes in the pH of the ascorbic acid-containing solution and changes in light and temperature, and in the presence of compounds such as surfactants, solvents and catalysts, in particular, metal catalysts.
Different means have been envisaged for stabilizing ascorbic acid. Japanese patents JP 89/115,558 and JP 83/129,892 teach the blocking of the reactive site of ascorbic acid, namely the hydroxyl site, by esterification and/or etherification with, for example, phosphated, sulphated and alkylated derivatives, and the use of these derivatives in cosmetic compositions to play the part of vitamin C. Unfortunately, these latter derivatives are much less effective than free vitamin C (without additional groups). Accordingly, the use of a vitamin C precursors has been envisaged.
Thus, European patent EP 487,404 discloses the use of a glucosyl derivative in dermatological compositions, capable of releasing the ascorbic acid when these compositions are brought into contact with the skin.
Moreover, the esterification of an ascorbic acid derivative and of a tocopherol derivative with phosphoric acid (see "Bioconversion of a vitamin to vitamins C and E in skin" by Kakuji Tojo and Aeric Lee published in J. Cosmet. Chem., 38, pages 333-339), and its use in a composition, have been envisaged. However, this diester displays lower efficacy than that of free ascorbic acid with respect to ascorbic acid and with respect to vitamin E, inferior antioxidant activity to that of free vitamin E.
This same problem is also encountered with any type of active agent.
It is also known, from EP-A-506,961, to use several derivatives of the same active agent in a cosmetic composition, but this document does not teach the enzymatic cleavage of these derivatives on the skin according to two different enzymatic mechanisms. Moreover, the efficacy of the combination described, ester and phosphate, is still insufficient.
Thus, a need remains for a cosmetic and/or dermatological composition containing vitamin derivatives or derivatives of any other active agent achieving the same efficacy as the compositions of free vitamins or active agents, as well as good stability of these vitamins or active agents.